I still haven't found a good way to get our big (46 million record) feature class to draw quickly in ArcGIS Explorer, even when zoomed in. In ArcMap at the same scale, things draw fine.
On the other hand, poking around the documentation, the contributed add-ins, and the SDK has turned up support for labeling, opening non-geometry tables, showing related records, and joining. A combination of third party and home coded add-ins should allow the software to handle what we could do with ArcView 3.3.
I think the thing that might get people interested in converting - maybe - is the integrated support for imagery. Right now the flow goes the other way - export shapefile to KML and load it up in a Google product.
I've uninstalled the beta so that I can test out some extensions that run on the released version.